The present invention relates to the extraction of metals by means of extraction agents constituted by propane diamides and it more particularly applies to the recovery of actinides and/or lanthanides present in the trivalent state in an acid aqueous solution, particularly in a nitric solution.
In irradiated nuclear fuel reprocessing installations, during the first uranium and plutonium extraction stage, aqueous solutions of fission products are obtained, which contain relatively large quantities of trivalent ions of lanthanides and actinides. The effluents from these installations also contain the same ions.
In view of the relatively long half-life of trivalent actinide elements, it is of great interest to separate them from nitric aqueous solutions in order to obviate the manipulation of effluents or waste having a high .alpha. activity. Hitherto, this separation has been carried out by solvent extraction using as extractants neutral or acid organophosphorus compounds, such as tributyl phosphate or di-2-ethylhexylphosphoric acid. However, the use of such extractants has not proved to be particularly advantageous, because their extraction yield with respect to trivalent ions is low and their industrial use leads to numerous problems due to the necessity of using large amounts of salifying agents, which increases the volume of the waste and the processing costs.
Consideration has also been given to the use for said separation of other neutral or bidentate organophosphorus compounds, such as diphosphonates and carbamyl phosphonates, together with amides, such as is described in J. Inorg. Nucl. Chem. 25, 1963, pp 883-892; J. Inorg. Nucl. Chem. 26, 1964, pp 1991-2003; and Separation Science and Technology, 15, 4, pp 825-844, 1980.
However, the results obtained are not satisfactory, particularly in the case of diamides such as tetrabutyl malonamide, because the extraction yields are very low.
However, research has been carried out on other diamides and it has been found that diamides of formula: ##STR2## in which R is an alkyl radical with between 2 and 10 carbon atoms make it possible to obtain satisfactory results, as described in French patent No. 2 537 326, filed on January 12, 1982 by the Commissariat a l'Energie Atomique. However, such diamides suffer from the disadvantage of mostly being in solid form, which leads to problems in connection with the use thereof.